Hi Staggy,
Is the ring on his leg a closed ring ? by this i mean a complete ring that can only be put on a very young baby, or is it a split ring,you will be able to see if there is a join in the ring where it has been shut together with closing pliers ?
If it is a split ring it could have been fitted at any time,if its a closed ring it would be put on at a few weeks old.
Baby greys will have dark eyes, that start changing gradually at around 6 months of age.
Also many baby greys have a dark tip to their red tail feathers, they loose this during the first molt.
Can you load a picture for us ?